1. Field of the Invention
The present invention relates to a flexible cable, a flexible cable mount method, an LED array head with a flexible cable, and an image forming apparatus with such an LED array head.
More specifically, the invention relates to a flexible cable for electrically connecting electrodes mounted on a first substrate and electrodes mounted on a second substrate, and a mount method for such a flexible cable.
The invention also relates to an LED array head with such a flexible cable and an image forming apparatus with such an LED array head for forming an image by electrophotography.
2. Related Background Art
A main trend in conventionally known print exposure LED array heads is to mount an LED array chip driver IC on the same substrate of glass epoxy on which an LED array chip, formed with silver foil patterns, is mounted. In such arrangements, it is necessary to perform wire bonding operations a number of times equal to the number of light emitting elements formed on an LED chip of a conventional LED array head, or equal to half the number. Also, it is difficult to form bonding pad patterns on the substrate. For these reasons, it is essential to form both the driver IC and LED array chip on the same substrate juxtaposed in one-to-one correspondence.
This type of print exposure LED array head having the driver IC on the same substrate as the LED array chip is, however, associated with the problem that electrical connection of wiring patterns becomes difficult because the number of wiring lines to be electrically connected increases as the resolution of an LED array chip, and thus its integration degree, is increased. In order to avoid this problem, a large substrate is used. However, a large substrate results in a large LED array head.
A compact LED array head has been realized by using two substrates: an LED array substrate on which an LED array chip is mounted; and a driver substrate on which an LED array chip driver IC is mounted, and by using a flexible cable for electrical connection of these two substrates. An LED array head has also been proposed which can make a printer more compact by reducing the size of the LED array chip for print exposure of a photosensitive member, and thereby reduce the size of the mechanical components around the photosensitive member. A flexible cable is made of resin and has wiring patterns formed on the resin.
Most of conventional flexible cables used by an LED array head are arranged such that a plurality of flexible cable units like the one shown in FIG. 1 are disposed in array along the LED array head. In FIG. 1, reference numeral 100 represents an LED array substrate, reference numeral 102 represents a driver substrate, reference numeral 104 represents flexible cable units, and reference numeral 106 represents an LED chip. Each of a plurality of flexible cable units 104 is mounted at a predetermined position between the LED array substrate 100 and drive substrate 102.
However, there are is increased number of mount steps for mounting a plurality of flexible cable units as compared to a single cable. The number of electrodes of each flexible cable unit of a high resolution LED array head is large, the pitch between electrodes becomes narrow, and a play area in the longitudinal direction of the LED array head is reduced. Therefore, a sufficient space between adjacent flexible cable units becomes difficult to engineer. To avoid this, a flexible cable such as the cable shown in FIG. 2 is presently used which is one continuous cable not divided into cable units and has an increased number of electrodes. In FIG. 2, reference numeral 200 represents an LED array substrate, reference numeral 202 represents a driver substrate, reference numeral 204 represents a flexible cable (single continuous type), and reference numeral 206 represents an LED chip. A cable similar to the flexible cable shown in FIG. 2 is disclosed, for example, in FIG. 1 of Japanese Patent Application Laid-open No. 11-123844.
In mounting a flexible cable of an LED array head arranged such that the LED array substrate and drive substrate are electrically connected by the flexible cable, however, a process which generates heat is necessary. Heat during the mount process causes thermal expansion or contraction of the flexible cable.
This thermal expansion or contraction of the flexible cable generates a small positional misalignment between electrodes formed on the flexible cable and electrodes formed on the driver substrate or LED array substrate. If the flexible cable is mounted by forcibly pulling it in order to correct the position misalignment of the electrodes of the flexible cable, a stress is applied to the LED array substrate that may warp the LED array disposed in a straight line. In this case, a direction of light exposure to the photosensitive member is curved so that a print line may be distorted in some cases.
It is an object of the invention to solve the above-described problems and provide a flexible cable capable of reliably connecting an LED array substrate and a driver substrate, a flexible cable mount method, an LED array head with such a flexible cable, and an image forming apparatus having such an LED array head.
It is another object of the present invention to provide a flexible cable capable of eliminating distortion of an LED array head by correcting an electrode pitch misalignment between an LED array substrate and a driver substrate caused by thermal expansion or contraction during thermal pressure bonding of the flexible cable, a flexible cable mount method, an LED array head with such a flexible cable, and an image forming apparatus having such an LED array head.
In order to achieve the above objects, the invention provides a flexible cable for electrical connection between electrodes on a first substrate and electrodes on a second substrate, comprising: a slit line to be used for removing a mechanical strain in the flexible cable generated when the first and/or second substrate is connected to the flexible cable; and a tear preventing round formed at an end of the slit line.
The slit line is used for correcting an electrode pitch shift caused by thermal expansion or contraction generated when the flexible cable is thermal-pressure bonded to the first or second substrate.
According to another aspect of the present invention, there is provided a method of mounting a flexible cable for electrical connection between electrodes on a first substrate and electrodes on a second substrate, comprising the steps of: connecting the flexible cable to the first and/or second substrate; and partially cutting the flexible cable from one end of the slit line to the other end of the slit line toward a tear preventing round formed at the other end of the slit line, the slit line being used for removing a mechanical strain in the flexible cable.
The slit line is used for correcting an electrode pitch shift caused by thermal expansion or contraction generated when the flexible cable is thermal-pressure bonded to the first or second substrate.
According to another aspect of the invention, there is provided an LED array head comprising the first substrate as an LED array substrate mounting an LED array; the second substrate as a driver substrate mounting a driver for driving the LED array; and the flexible cable with the slit line, the flexible cable connecting the LED array substrate and the driver substrate.
The slit line is used for correcting an electrode pitch shift caused by thermal expansion or contraction generated when the flexible cable is thermal-pressure bonded to the first or second substrate.
According to another aspect of the present invention, there is provided an image forming apparatus for forming an image through electrophotography, the apparatus comprising the LED array head.
According to another aspect of the invention, there is provided an image forming apparatus for forming a latent image on a photosensitive member by applying light to the photosensitive member, comprising: an LED array head for exposing the photosensitive member, the LED array head comprising: an LED array substrate mounting at least one LED array chip in an array shape, the LED array chip having at least one LED disposed in an array shape and formed on a semiconductor wafer for exposing the photosensitive member; a driver substrate mounting a driver IC for driving the LED chip array upon reception of an image signal; and a flexible cable for electrically connecting the LED array substrate and the driver substrate; and a slit formed in the flexible cable for correcting an electrode pitch shift between the LED array substrate and the drive substrate caused by thermal expansion or contraction generated when the flexible cable is thermal-pressure bonded.
According to another aspect of the present invention, there is provided an LED array head for use with an image forming apparatus for forming a latent image on a photosensitive member by applying light to the photosensitive member, comprising: an LED array substrate mounting at least one LED array chip in an array shape, the LED array chip having at least one LED disposed in an array shape and formed on a semiconductor wafer for exposing the photosensitive member; a driver substrate mounting a driver IC for driving the LED chip array upon reception of an image signal; and a flexible cable for electrically connecting the LED array substrate and the driver substrate, wherein a slit is formed in the flexible cable for correcting an electrode pitch shift between the LED array substrate and the drive substrate caused by thermal expansion or contraction generated when the flexible cable is thermal-pressure bonded.
When an electrode pitch shift between the LED array substrate and the drive substrate caused by thermal expansion or contraction generated when the flexible cable is thermal-pressure bonded, is to be corrected, the slit is inserted into an area of the flexible cable where the electrode pitch shift occurred after the thermal-pressure bonding.
The area the slit is inserted for correcting the electrode pitch shift caused when the flexible cable is thermal-pressure bonded, is formed with a designation for the slit, and a tear preventing round is formed in advance in order to prevent the flexible cable from being torn when the slit is inserted.
According to another aspect of the invention, there is provided an image forming apparatus having the LED array head described above.
According to another aspect of the present invention, there is provided a method of mounting an LED array head for use with an image forming apparatus for forming a latent image on a photosensitive member by applying light to the photosensitive member, comprising the steps of: electrically connecting an LED array substrate mounting at least one LED array chip in an array shape, the LED array chip having at least one LED disposed in an array shape and formed on a semiconductor wafer for exposing the photosensitive member and a driver substrate mounting a driver IC for driving the LED chip array upon reception of an image signal, by using a flexible cable; and forming the flexible cable with a slit for correcting an electrode pitch shift between the LED array substrate and the drive substrate caused by thermal expansion or contraction generated when the flexible cable is thermal-pressure bonded.
When an electrode pitch shift between the LED array substrate and the drive substrate caused by thermal expansion or contraction generated when the flexible cable is thermal-pressure bonded, is to be corrected, the slit is inserted into an area of the flexible cable where the electrode pitch shift occurred after the thermal-pressure bonding.
The area the slit is inserted for correcting the electrode pitch shift caused when the flexible cable is thermal-pressure bonded, is formed with a designation for the slit, and a tear preventing round is formed in advance in order to prevent the flexible cable from being torn when the slit is inserted.